The overall goal of this protocol is to develop and evaluate a set of non-virologic diagnostic algorithms that can be used to monitor HIV-exposed children of unknown infection status for treatment eligibility during the first 12 weeks of life, with validation of our model among HIV-exposed children up to 12 months of age. We will evaluate the performance of different algorithms in two separate but common scenarios in Africa: (1) where infant PCR testing is not available, and (2) where infant PCR may be available, but poorly accessible due to cost and resource considerations. Although DNA PCR testing has become available in Zambia, only three sites currently provide this type of testing and capacity may be limited for country-wide screening. Our study was designed to determine HIV infection and antiretroviral therapy (ART) eligibility using more commonly used "non-virologic" tests, such as CD4, CD8, HIV antibody, total lymphocyte count, hemoglobin, and clinical staging. Previous studies have demonstrated that these indicators by themselves do not perform well in the absence of DNA PCR testing. In this exploratory study, we hypothesize that combinations of these tests - in formalized algorithms - can yield high performance and be used in rural settings where reliable DNA PCR services are not yet available or remain limited.